218 ANIMAL LIFE PAST AND PRESENT. 



so that the depth of the intervening valleys is like- 

 wise increased. These valleys also contain a certain 

 amount of the third constituent of mammalian teeth 

 the cement so that their bases are partially filled up 

 by it. 



From the teeth of these Intermediate Elephants, as 

 they may be conveniently called, the step is but very 



FIG. 75. A left upper cheek-tooth of a Mastodon in an unworn condition. 



short to those of the modern or true Elephants. In 

 these, as shown in Fig. 77, the difference from the 

 teeth of the Mastodon is so great that without the 

 intermediate forms it is difficult to trace the corre- 

 spondence between their respective elements. In the 

 true Elephants, indeed, the transverse ridges of the 

 teeth have not only been greatly increased in number, 

 so that there may be as many as twenty-five in the 



